Stack switch construction



@am M, 19430 v. H. HARDY 2,3299266 I STACK SWITCH CQNSTRUC'TIOXI Film oct; 17,"1941 Patented Sept. 14, 1943 STACK SWITCH CONSTRUCTION Vaughn H. Hardy, Rochester, N. Y., assignor to General Motors Corporation, Detroit, Mich., a

corporation of Delaware Application October 17, 1941, Serial No. 415,338

(Cl. 20c- 138) 7 laiins.

This invention relates generally to thermally actuated electric switches and more particularly to improvements in that type of switch which is known as a stack switch for use in a Control system for fluid fuel burners.

Although the present embodiment is shown and described as a stack switch it will be apparent that the Switch mechanism, as a whole or in part, may be used in other applications wherein it is desired to control an electric circuit or operate an electric switch by temperature changes.

One object of the invention is to provide a switch mechanism of simple construction which is positive and reliable in operation and in which ie switch contacts will be opened or closed immediately upon initial expansion or contraction of the thermal element and continued expansion or contraction will not affect the position cf the switch contacts.

A further object is to utilizev a thermal element of a type which expands and contracts axially et a much more .rapid rate than thermal elements heretofore used in switches Of this type and thereby permit the use of a Simplified switch in which a pivoted lswitch arm Carrying a contact is operated directly through a simple friction drive by a rod connected to the thermal element.

The foregoing and other objects and features of the invention together with the advantages thereof will be apparent Or will be specifically pointed out in the description of the embodiment illustrated in the accompanying drawing in which:

Figure 1 is a fragmentary, longitudinal Sectional view of my improved stack switch.

Figure 2 is an enlarged fragmentary, front elevation of the stack switch.

Figure 3 is a sectional View taken substantially on line 3-3 of Figure 2.

Figure fi is an enlarged, fragmentary perspective of a portion of the thermal element.

Referring first to Figure l, there been shown therein a base plate 2 on which the several elements of the oil burner control unit may be mounted with a bracket 4 secured to the plate 2 and spaced from the rear side thereof by means such as post 6. A tube 8 is secured to bracket 4 and extends rearwardly therefrom and the control unit is adapted to be mounted in any desired manner on a .combustion Chamber wallv or furnace flue with the tube 8 extending into the combustion chamber Or flue so' that a thermal element adjacent the inner end'of the tube -will be subject to the .temperature of the combustion or kflue gases as will be hereinafter described.

A switch operating rod `Ill extends within the tube 8 with its inner end connected to the thermal element l2.. As shown in Figures 1 .and 4 this thermal element AI2 consists of a bimetal kdouble helix coil in which the integrally joined Stripsof metals having different coefficients of thermal expansion are first wound into a small ycoil or helix which is then wound axially into a larger coil or helix. As so constructed it will be apparent that on temperature changes the t smallccil or helix will tend to expand or contract along its axis and result in a rapid expansion yor contraction of the larger coil or helix in the direction of its axis which is utilized in the manner hereinafter `described to move the rod I0 axially to operate `the Switch. In the present instance, the bimetal strip is initially Wound with the metal having the greater coeflicient of thernml expansion on the outer side of the small coil or helix so that the resulting thermal element kas a Whole will expand axially along its axis when heated and contract axially on cooling.

As noted abo-ve, the rod Ill is lconnected at its inner end to the `thermal element I 2. As shown in Figure l the inner end of the rod I0 is formed with a longitudinal groove extending from the end thereof to a recess I4 and ,the adjacent axially extending end of the thermal element I2 is received within the groove and has the extreme end thereof bent to extend into the recess I4. A sleeve -Il extends around the end of rod I0 and is crimped into an annular groove I8 in `the rod to hold the bent end of the thermal Y element in interlocking engagement with the rod.

The other axially extending end Of the thermal element I2 is similarly formed with the extreme y end thereof bent to engage within an 'Opening in the vangular portion 20 of the tube 8 with means such as the rivet 2v2 extending through the opening and ongaging'the end of the thermal element to thereby securely interlock the same to the ytube '8. y It `will be noted that the inner end of ^through enlarged, aligned openings in bracket 4 and base plate 2 and is provided intermediate its ends within `the tube 8 with a shoulder 24 engaged by the conical spring 25 which extends between this shoulder and a stationary member 28 in tube 8. The spring 26 is relatively weak and is provided to exert a slight tension at all times on the rod I9 and thermal element I2 so that the rod will respond immediately to any axial expansion or contraction of the thermal element.

Referring now to the switch construction, the same is preferably constructed as a separate unit which may be assembled and then mounted on the base plate 2. The switch housing indicated generally at 3i) is formed as a channel with a rear wall 32 adapted to be secured as by rivets to the base plate 2 and with parallel side Walls 34 and 36. Extending between the side walls 34 and 35 is a pin 38 serving as a pivotal mounting for an angular bracket to which is secured as by rivets a contact arm 42 of insulating material. An electric terminal plate 44 and the lower end of a spring contact blade 46 are secured to the outer side of the contact arm 42 adjacent the bracket 40 by rivets 43.

As shown in Figure 2, the central portion of the spring contact blade 4S is cut away to form upwardly extending spring arms which are inte- K grally joined at their upper ends to receive the reduced riveted end of a contact 50 extending through an opening in the contact arm 42 adjacent the upper end thereof. The contact 50 is adapted to cooperate with a stationary Contact 52 riveted to angle bracket 54 which is secured to and insulated from the side wall 34 of housing 30 by rivets 56 and insulating plates 58 and provided with the terminal connecting arm 60.

The contact arm 42 is provided between its y upper and lower ends with a vertically elongated opening 62 for the switch operating red i0 which extends loosely through this opening, and a vertically movable member is mounted on the inner side of the contact arm 42 to frictionally engage the rod l0 whereby axial movement of the rod Will rotate the Contact arm to open or close the contacts. This member preferably consists of a graphite brush 64 mounted to slide vertically in a guide constituted by the arm 42 and channelshaped brush holder 66 which may be secured on the inner side of the contact arm 42 by tongues 68 extending through arm 42 with the ends thereof bent over to engage the outer side of the arm as shown in Figure 2. resiliently forced upwardly into constant frictional engagement with the rod I0 by the coil spring l0 interposed between the brush and an abutment such as a Cotter pin 12 extending between opposite walls of the brush holder 66.

Upward movement of the outer end of the rod I0 in a direction away from the brush 64 is prevented by the anti-friction pulley 14 which is freely rotatable on the shaft 16 extending between the side walls 34 and 36 of the housing 30.

On reference to Figure 1 it will be seen that as the contact arm 42 is moved in a direction to close the contacts the further movement of the arm in this direction will be limited by engagement of the arm with the enlarged contact head of Contact 5U, and an adjustable means is provided to limit the movement of the contact arm in the opposite direction on opening of the contacts. This means consists of the stop arm 18 having an intermediate portion 80 extending transversely from adjacent the side Wall 36 of housing 3S to approximately the center of contact arm 42 with the end of portion 60 enlarged in the direction of arm 42 to engage therewith The brush 64 is without contacting the adjacent portion of spring contact blade 46.

The step arm 18 is pivotally connected at its lower end to the housing side wall 36 by means o! an outwardly and downwardly bent tongue 82 extending through an opening in the side wall and the upper end of the stop arm extends vertically through a slot formed on the inner side of Wall 36 by pressing a cut-out portion 84 of the Wall inwardly as shown in Figures 2 and 3. The arm 18 is constructed of spring metal and the upper end bent away from the side wall 36 to frictionally engage the cut-out portion I4 which may be formed with relatively sharp corrugations 36 to cooperate with a vertical rib 6l on the adjacent portion of arm 18 to retain the arm in its adjusted position. The upper end of the stop arm I8 extends above the side wall 36 to provide a handle so that the arm may be manually rotated about its pivot connection to the side wall to adjust the location of the portion of the stop arm with reference to the contact arm 42.

With reference to the operation of the stack switch, the contacts 5U and 52 have lbeen shown as closed in Figure 1 which is the normal position when the iiuid fuel burner is not :In operation. Assuming now that the burner is started, the heat of combustion or ue gases will cause an immediate expansion of the thermal element l2 to move the rod I0 axially to the left and the frictional engagement of the graphite brush 64 with the rod will cause an immediate movement of the contact arm 42 about pivot 38 in a direction to carry the contact 53 away from contact 52. After opening the contacts the arm 42 will continue to move with rod I0 until the arm engages the portion 80 of the stop arm 18 whereupon any further expansion of the thermal element and axial movement of the rod will result in a sliding of the rod on the graphite brush 64 without any further separation of the contacts.

When the burner stops and the temperature of the combustion or flue gases falls, tbe thermal element I2 will immediately contract to move the rod I0 axially tothe right and the frictional engagement of the graphite brush 64 with the rod will cause an immediate movement of the contact arm 42 about pivot 38 in a direction to move the contact 50 into engagement with contact 52. The length of time before actual engagement of the contacts will be relatively short and will be dependent upon the manually adjusted position of the stop arm 18 which limits the extent of separation of the contacts as has been described. After contact 50 engages contact 52, the contact arm 42 Wil move only until it engages the enlarged head of contact 50 whereupon any further contraction of the thermal element and axial movement of the rod to the right will result in a. sliding of the rod on the graphite brush 64.

It will therefore be apparent that by limiting the movement of the Contact arm 42 and providing the friction drive between rod lli and contact arm 42, the switch contacts will be opened or closed substantially immediately upon any initial rise or fall in temperature, such as causes expansion or contraction of the thermal element, regardless of the extent of actual temperature changes. It should be noted, however, that extremely small changes in temperature such as minor fluctuations may not move the contact arm 42 a sufficient distance to open or close the contacts in view of the spring blade mounting of contact 50 on the contact arm 42 and the adjustable extent of separation of the contacts afforded by the stop arm 18.

It is also desired to note that by reason of the relatively great length of the bimetal strip that is incorporated in the compact double helix coil, this thermal element will not only respond immediately to temperature changes but Will expand or contract at such a rapid rate that the switch contacts will be opened orclosed without appreciable sparking Whereas in prior stack switch construction utilizing a relatively slow acting thermal element or elements it has been found necessary to provide some form of snap action mechanism to operate the movable switch contact.

Whereas the thermal element has been described herein as adapted to expand when heated it will be apparent that the same may be formed, if desired, by winding the metal hav-- ing the greater coeflicient of thermal expansion on the inner side instead of the outer side of the initially formed small coil or helix so as to contract when heated and the switch contacts would then be closed on rise in temperature and opened when the temperature falls. It will also be understood that whereas the present embodiment has been shown and described as a stack switch, the several features thereof are not in any way limited to this particular application but may be variously employed in many known types of temperature controls.

Many changes and modifications in the specific construction disclosed herein will Ibe apparent to those skilled in the art and are contemplated as within the scope of my invention as set forth in the claims.

I claim:

1. In a thermally operated switch, a thermal element, a rod movable axially by said thermal element in response to temperature changes, cooperating contacts, and means whereby one of said contacts may be moved into and out of engagement with the other contact upon axial movement of said rod including a pivoted arm on which said movable contact is mounted, a friction element mounted on said arm, spring means to force said element into engagement with one side of said rod, and a xed rotatable pulley adapted to engage the opposite side of said rod.

2. In a thermally operated switch, a switch operating rod, switching means operated by movement of said rod, a bimetal member having one end thereof fixed and the other end thereof movable in response to temperature changes, and means to connect the movable end of said bimetal member to said rod including a groove inA said rod adjacent the end thereof adapted to receive the end of said member, and a sleeve extending around said rod to retain said end in said groove.

3. In a thermally operated switch, a switch operating rod, switching means operated by movement of said rod, a bimetal member having one end thereof movable in response to temperature changes and connected to said rod, and means to connect the other end of said bimetal member to a iixed support including an opening in said support with the end of said bimetal member bent to extend into said opening, and a rivet passing through said opening and engaging the bent end of said bimetal member.

4. In a thermally operated switch, a thermal element comprising a bimetal double helix coil adapted to expand and contract axially in response to temperature changes, a rod connected to one end of said coil and movable axially thereby, a switch casing, a relatively fixed contact mounted on said casing and a contact adapted to be moved into and out of engagement therewith, means for mounting said movable Contact including a contact arm which is pivotally connected to said casing adjacent one end of said arm and carries said contact adjacent its other end, means to adjustably limit the extent of pivotal movement of said arm, and means to move said contact arm upon axial movement of said rod including a graphite brush mounted on said arm and spring means also mounted on said arm and forcing said brush into frictional engagement with said rod.

5. In a thermally operated switch, a thermal element, a rod movable axially by said thermal element in response to temperature changes, a switch casing, a relatively fixed contact mounted on said casing and a Contact adapted to be moved into and out of engagement therewith, means for mounting said movable contact including a contact arm which is pivotally con` nected to said casing adjacent one end of said arm and carries said contact adjacent its other end, and means to move said contact arm upon axial movement of said rod including a graphite brush mounted on said arm and spring means also mounted on said arm and forcing said brush into frictional engagement with said rod.

6. In a thermally operated switch, a thermal element, a rod movable axially by said thermal element in response to temperature changes, a switch casing, a relatively fixed contact mounted on said casing and a contact adapted to be moved into and out of engagement therewith, means for mounting said movable contact including a contact arm which is pivotally connected to said f casing adjacent one end of said arm and carries said contact adjacent its other end, means to move said arm upon axial movement of said rod including a friction connection between said arm and said rod, and means to adjustably limit the extent of separation of said contacts including a manually adjustable member pivotally mounted on said casing having a portion thereof extending into the path of movement of said contact arm,

'7. The elements set forth in claim 6 in which means is provided to frictionally retain said manually adjustable member in any one of a plurality of positions to which the same may be adjusted.

VAUGHN H. HARDY. 

